Self clean oven with delayed opening valve

ABSTRACT

A gas-fueled oven having first and second burners therein, conduits connected to the respective burners, and electrical valve means connecting said conduits to a common source of fuel, said valve means comprising a pair of electrically-operated bimetallic closure devices one associated with each conduit, said devices being operable when simultaneously energized to open said conduits at different time intervals whereby one of said burners will be supplied with fuel and ignited at a predetermined time interval subsequent to fueling and ignition of the other burner.

United States Patent 1191 Kemp [ Oct. 28, 1975 SELF CLEAN OVEN WITH DELAYED OPENING VALVE [75] Inventor: Wayne T. Kemp, Kutztown, Pa.

[73] Assignee: Raytheon Company, Lexington,

Mass.

22 Filed: Sept. 27, 1974 21 Appl. No.: 510,107

[52] U.S. Cl 126/273 R; 126/21 R; 236/15 A [51] Int. Cl. F24C 15/02 [58] Field of Search 126/19, 21, 273, 39 C;

[56] References Cited UNITED STATES PATENTS 4/1971 Branson et a1 236/15 A X 5/1972 Ray 236/15 A 3,692,239 9/1972 Genbauffe 236/15 A Primary ExaminerEdward G. Favors Attorney, Agent, or Firm-Harold A. Murphy; Joseph D. Pannone; John T. Meaney [57] ABSTRACT A gas-fueled oven having first and second burners therein, conduits connected to the respective burners, and electrical valve means connecting said conduits to a common source of fuel, said valve means comprising a pair of electrically-operated bimetallic closure devices one associated with each conduit, said devices being operable when simultaneously energized to open said conduits at different time intervals whereby one of said burners will be supplied with fuel and ignited at a predetermined time interval subsequent to fueling and ignition of the other burner.

16 Claims, 5 Drawing Figures US. Patent Oct. 28, 1975 Sheet 2 of3 3,915,149

SELF CLEAN OVEN WITH DELAYED OPENING VALVE BACKGROUND OF THE INVENTION In the construction of a conventional gas-fueled selfclean oven there are provided two separate burners, a broil burner located in the upper regions of the oven cavity and a bake burner positioned at the bottom of the oven. The interior of the oven is cleaned by operating both burners to create a temperature within the oven which is high enough for pyrolysis of grease, spillovers, or other undesirable accumulations on the oven walls.

The self-clean cycle is initiated by operation of suitable switching means which opens a gas valve to supply gas to both burner elements whereupon they become ignited to perform their function. However, it has been found that if both burners are ignited substantially simultaneously the upper burner will operate in an unstable manner and actually may become extinguished by the upward flow of combustion products from the lower burner. This is, of course, an undesirable condition which has been overcome by providing separate electrically controlled valve means for each burner element with a time delay relay being utilized in the lower bake burner electrical circuit to delay ignition of the bake burner element until the upper broil burner element has operated for a sufficient length of time for it to have stable flames and provide a stack action in the oven compartment. Then when the bake burner is operated, its flue product flow will not detrimentally affect the upper burner operation.

Such control of the ignition cycles for the two burners involves the use of separate valves and electrical circuitry including a time delay relay. This results in an undesirable increase in costs in the highly competitive manufacture of appliances such as ranges and ovens.

SUMMARY OF THE INVENTION The present invention overcomes the foregoing and other objections to the known prior art by the provision of a self-clean oven wherein electrically operated valve means is provided for controlling the flow of fuel to two separate burners and wherein said valve means includes within itself means for delaying the flow of fuel to one of the burners for a predetermined time interval subsequent to operation of the second burner.

This is accomplished according to this invention by the provision of valve means wherein the valve actuators include in part bimetallic structures and heating elements associated therewith designed to effect operation of the actuators at different time intervals. To achieve this, the heating elements may be substantially similar but the actuator arms may be differently fabricated or constructed so that one arm applies a greater pressure upon the valve seat than the other and therefore requires a longer time interval for the heating and bimetallic elements to overcome the increased pressure before effecting movement of the valve seat. In a second embodiment of the invention the heating elements are of different sizes so as to effect operation of the bimetallic elements and, consequently, movement of the actuator arms and valve seats at different time intervals.

In either embodiment, the valve actuator associated with the lower bake burner is made to operate at a selected time interval, such as 30 seconds, after the other actuator has been operated to supply fuel to the upper broil burner.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings wherein;

FIG. I is a front elevational view of a range having a self-clean oven and wherein a portion of the front of the oven is removed to show the invention;

FIG. 2 is a side elevation of the range shown in FIG. 1 with a side thereof broken away to show the invention;

FIG. 3 is a diagrammatic illustration showing the burners, gas supply conduits and valve means of the invention;

FIG. 4 is an enlarged sectional view of one embodiment of the valve means including a schematic electrical circuit; and

FIG. 5 is a view similar to FIG. 4 illustrating another embodiment of the valve means with the circuit omitted.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawings, wherein like characters of reference designate like parts throughout the several views, the gas range 10 depicted in FIGS. 1 and 2 is shown without the top burners and gas supply connections thereto which do not in themselves constitute any part of this invention. More particularly, the range 10 comprises an upstanding substantially box like metal body 12 carrying a substantially horizontal metal cooking top 14 and upstanding backsplash l6 and sidesplashes 18 arranged respectively at the back and sides of the cooking top 14.

Within the body 12 is a substantially box-shaped metal liner 20 which defines an oven cavity 22 and comprises a rear wall 24, a top wall 26, a bottom wall 28, and a pair of side walls 29.

An opening is provided in the front of the range and through the liner front wall 30, whereby the interior of the oven cooking cavity 22 is accessible from the front of the body. A door 32 is mounted upon the front of the body 12 by a suitable hinge structure (not shown) whereby the door is pivotally movable into open or closed relation with respect to the open front of the oven cavity 22. The door hinge, and latching structure are not shown and do not constitute in themselves part of the present invention.

The liner top wall 26 is spaced well below the cooking top 14 and heat-insulated therefrom by a bolt 34 of fibrous glass or other selected insulating material which is intended to aid in confining heat as much as possible to the interior of the cavity 22 during operation of the oven. The door 32 may be similarly filled with insulating material 36, and at the back of the range an insulating rear wall or shield 38 is provided in spaced relation with the oven rear wall 24, and the space therebetween is also filled with insulation 40. Thus, the top, sides, rear and front of the oven are insulated from the adjacent portions of the range and from the exterior atmosphere. At the bottom of the range is a heat-reflecting shield or plate 42, provided for reflecting heat toward the oven 20 and thus serving to protect the floor beneath the range.

There is provided a lower burner 44 which is located in the cavity 46 beneath the liner bottom wall 28 and above shield 42. Burner 44 extends a substantial distance across the width of the cavity 46 and is of a conventional blue-flame type which includes a ported burner head 48 having a gas-receiving chamber for receiving gaseous fuel from a venturi or the like 50. A constantly burning pilot 55 is suitably connected into the gas supply system, as will be described, and is located adjacent the burner head 44 so that jets of flame will be ignited at each of the ports in the head when the control system to be described is operated to allow gas to flow into the head.

The lower burner head 44 is enclosed within the cavity 46 on the bottom and sides by a heat-reflecting shield 56, the bottom of which is mounted above and spaced from shield 42 and which has side portions or wings 58 angled upwardly and outwardly to deflect heat toward the bottom wall 28 of the oven liner 20.

Suitable vents 60 and 61 are, of course, provided in the shields 56 and 42 to insure that sufficient air enters the cavity 46 to sustain combustion.

The burner head 48 is provided with longitudinally spaced ports so that upon operation a number ofjets of blue flame will project outwardly from the respective ports in the normal manner ofa burner of this type. The control system may include one of a group of switches controlled by knoHs 63 which is suitably connected to valve means for controlling the flow of gas to the lower ported burner 44 and to an upper radiant burner 64.

The radiant burner 64 is in the oven cavity at the upper exteremity thereof and is of a type which produces a broad sheet of flame or incandescence. One example of a radiant burner of a type suitable for use in the self-clean oven of the present invention is that disclosed in U.S. Pat. No. 3,122,197. This burner comprises a device wherein gas is burned on the surface of a screen to heat the screen to incandescence. Such a radiant burner 64 includes a burner head 66 defining an opensided cavity, and a mixing chamber such as a venturi 68 (FIG. 2) which has its inner end communicating with the burner cavity and the outer end 70 adapted to receive gas from pipe 72. The mixing chamber 68, for efficient and rapid combustion, is required to receive an ample supply of primary combustion air. For example parts of air to one part of gas is considered to be one satisfactory ratio in the case of natural gas. To insure an adequate supply of uncontaminated primary combustion air, the mixing chamber 68 is made in the nature of an oversized venturi as shown in FIG. 2.

The burner 64 also includes an assembly 76 of a number of screens, as described in the aforementioned U.S. Patent, which screens close the open side of the burner cavity, this being the lower surface or side when the burner 64 is positioned in the upper extremity of the oven cavity 22 as shown. It will be apparent that a radiant burner 64 may be made which will produce an extremely broad, substantially continuous flame or incandescence which covers a substantially large radiating area.

The pipe 72 is connected to a supply line 52 through a valve means 84 to be described and is also connected into the control system so that, when the control system is operated to allow gas to flow from pipe 72 into mixing chamber 68, where it becomes mixed with air, and then into burner head 66, it will become ignited by a constantly burning flame of a pilot light 78. This creates a broad flame which radiates infrared energy throughout the oven cavity.

It will be noted that primary air is provided for the radiant burner head 64 by means of a duct 80 which extends upwardly along rear wall 38 and terminates at its upper end at the opening 81 into which the end of the mixing chamber extends. Since the lower end of the duct terminates in the lower regions of the range, a constant supply of uncontaminated air is allowed to pass into the burner head 64. The lower end of duct 80 is shown as terminating at an opening 82 which communicates with the region of the range beneath the lower heat shield 42.

It will be understood, as pointed out before, that the burners 44 and 64 may be operated individually and separately from one another for conventional baking and broiling operations. However, both burners are operated simultaneously for performing a self-cleaning operation, although the upper burner must be operated for a short time before the lower burner at the start of a self-cleaning operation, and one or both burners may be intermittently operated or modulated during a selfcleaning cycle in order to maintain a required temperature level.

The gas supply line 52 is adapted to be connected to any suitable source of gaseous fuel at one end, and at its other end is connected directly to feed lines 86 and 86a by which fuel is constantly supplied to the respective pilots 55 and 78. Thus the pilots are enabbled to keep constantly burning. However, electric ignition may be provided, if desired, in place of the pilots.

In accordance with the present invention the ignition of the lower burner 44 is made to occur at some selected time interval, such as 30 seconds, for example, after ignition of the top burner 64. This is accomplished by the novel valve means 84 which is directly coupled as by inlet member 88 to the gas supply line 52. The valve means 84 comprises a housing 90 with the interior of which member 88 communicates so that gas is constantly supplied into the housing.

Two oppositely disposed outlet members 92 and 94 are also connected to housing 90 as shown best in FIGS. 3-5. Member 92 is coupled to the adjacent end of pipe 72 by which gas is supplied to the upper burner 64. Member 94 is coupled to a pipe 96 which feeds gas into the venturi 50 which extends from one side of the lower burner 44. Thus both burners 44 and 64 may be supplied with gas from within the housing 90 of valve means 84, since each member 92 and 94 communicates directly with the interior of the housing 90 by a respective opening therein (not shown).

Included within housing 90 are two valves 98 and 100. Valve 98 includes a valve seat 102 of rubber or the like which is held firmly over the opening in member 92 by an arm 104 to which it is attached. The other end of arm 104 is rigidly supported upon the housing wall as by block 106. At least a portion 108 of arm 104 is a bimetal stucture which is encircled by or otherwise disposed adjacent a heating coil 110. Coil 110 has one end connected to a conductive stud 112 which extends insulatingly through the housing wall and which also serves to anchor a terminal 114 on the outside of the housing. The other end of coil 110 is attached to a metal clip 116 which is in turn conductively secured by stud 118 which also extends insulatingly through the housing wall and serves to support block 106 on the inside of the housing and to anchor a second terminal 120 to the outside of the housing.

The second valve 100 is constructed generally similar to valve 98, including valve seat 102a, arm 104a, bimetal portion 108a, heating coil 1 a, block 106a, clip 116a, studs 112a and 118a, and terminals 114a and 120a. Seat 102a normally is held in closing relation to the opening in the inner end of member 94.

The terminals 114, 120, 114a and 120a are all connected by conventional circuitry through a switch 122 to a source 124 of electrical potential SC (FIG. 4) so that when the self-clean cycle is started, such as by operation of the selected control knob 63 and/or latching of the oven door, and resultant operation of the switch 122 as is well known, the coils 110 and 110a will become simultaneously heated. Heat from the coils will be transferred by radiation to the respective bimetal structures 108 and 108a, whereupon the arms 104 and 104a will be moved in response to bending of the bimetal structures when heated. This movement of the arms 104 and 104a will pull the valve seats 102 and 102a away from the outlet members, allowing gas to flow to the burners.

However, in accordance with this invention, it is intended that the top burner 64 be supplied with gas, ignited and operated for a selected length of time such as, for example, thirty seconds before gas is supplied to the lower burner 44. This is done by causing the valve 100 to open later than the valve 98. One way of doing this is shown in FIG. 4 and comprises structuring the valve 100 so that in normally closed conditions a greater force is exerted upon the valve seat 102a than is the case with valve 98. For example, a force of about four ounces may be applied to maintain valve 98 closed, which force is relatively easily overcome by heating the bimetal portion 108 to open the valve within about 2 to 5 seconds. However, a force of about 8 ounces, for example, is applied to valve seat 102a, as indicated by curvature of arm 104a, and this extra pressure must be overcome before the valve seat 102a will separate from the outlet member 94. This may require a time interval of about 30 seconds or more. The structure of FIG. 4

assumes that the bimetal devices 108 and 108a are similar, as well as the heating coils 110 and 110a.

Difference in time intervals for operating the respective valves 98 and 100 may be achieved in other ways, such as by providing the coils 110 and 1 10a with different heating capabilities. For example, as shown in FIG. 5 the heating coil 110 is of a size somewhat larger than the coil 110a and, therefore, it will heat the bimetal element 108 much quicker than the small coil 110a will heat bimetal element 108a. Thus, valve 98 will operate in a relatively short time to supply gas to the upper burner 64, but valve 100 will operate much slower so that gas will not be supplied to burner 44 until a selected time interval has passed. As a result of such delay in the operation of the lower burner 44, the upper burner 64 will be given the opportunity to stabilize to the point where subsequent operation of the lower burner will not detrimentally affect the efficient operation of the upper burner.

Furthermore, a valve means such as described provides in itself the ability to provide controlled time sequence operation of the two burners in a simple, efficient, economical and straightforward manner without the requirement for separate electrical time delay means.

It is to be understood that while the valve means shown in FIGS. 4 and 5 comprises a single casing housing two separate valves, the valve means within the purview of this invention could comprise two separate casings or housings each of which contains respective valves 98 and 100. In such a case it is merely necessary to insure that both heating coils and 110a will be activated simultaneously since to do otherwise would require the use of some sort of accessory time delay device.

From the foregoing, it will be apparent that all of the objectives of this invention have been achieved by the gas fueled self-cleaning oven and fuel control system disclosed herein. It will be understood, however, that several modifications in the invention and its manner of use may be made by those skilled in the art without departing from the spirit of the invention as expressed in the accompanying claims. Therefore, all matter shown and described is to be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A gas-fueled oven comprising a compartment to be heated, two spaced burners for heating said compartment, and means for supplying fuel to the burners at different time intervals, said'means comprising valve means having inlet port means connected to a source offuel, a pair of outlet port means, conduits connecting the outlet port means to respective burners, and a pair of electrically operated valves disposed in operative normally closed relation to respective outlet port means, and means for supplying electric potential to said valves simultaneously, one of said valves being operable at a predetermined time interval subsequent to the other. 7

2. A gas-fueled oven comprising a. compartment to be heated,two spaced burners for heating said compartment, and means for supplying fuel to the burners at different time intervals, said means comprising valve means having inlet port means connected to a source of fuel, a pair of outlet port means, conduits connecting the outlet port means to respective burners, a pair of electrically. operatedvalves disposed in operative normally closed relation,to respective outlet port means, said valves having different controlled operating characteristics whereby one thereof will open at a predetermined time interval subsequent to opening of the other, and means for supplying electrical potential to said valves simultaneously.

3. A gas-fueled oven comprising a compartment to be heated, two spaced burners for heating said compartment, and means for supplying fuel to the burners at different time intervals, said means comprising valve means having inlet port means connected to a source of fuel, a pair of outlet port means, conduits connecting the outlet port means to respective burners, and a pair of valves each having a closure member disposed in operative normally closed relation to a respective outlet port means, a supporting member supporting said closure member and including a bimetallic element and means for heating the individual bimetallic elements to cause movement of said supporting members and consequent retraction of the closure members from the respective outlet port means.

4. A gas-fueled oven as set forth in claim 3 wherein one of said supporting arms and closure members is retractable from the respective outlet port means at a predetermined time interval subsequent to retraction of the other arm.

5. A gas-fueled oven as set forth in claim 4 wherein means is provided for supplying electrical potential to said heating means simultaneously.

6. A gas-fueled oven as set forth in claim 3 wherein said pair of valves are located within a common housing.

7. A gas-fueled oven as set forth in claim 3 wherein one of said closure members engages its respective outlet port means with a pressure substantially in excess of the pressure with which the other closure member engages its respective outlet port means whereby the closure member applying greater pressure will require a longer period of time for movement away from its outlet port means.

8. A gas-fueled oven as set forth in claim 3 wherein said heating means comprises a pair of electrically energizable resistance heating elements located adjacent respective bimetallic elements.

9. A gas-fueled oven as set forth in claim 8 wherein one of said heating elements is larger than the other whereby it will function to heat its adjacent bimetallic element faster than the smaller heating element can heat its respective bimetallic member.

10. A self-clean oven comprising an oven compartment to be heated, a first gas-fueled burner in the upper portion of the compartment, a second gas-fueled burner in the lower portion of the compartment, piping adapted to be connected at one end to a source of fuel and connected to said burners for supplying fuel thereto, ignition means adjacent each burner, and control means for delaying the supply of fuel to said second burner for a predetermined time interval subsequent supply of fuel to said first burner, said control means comprising valve means in said piping, said valve means having inlet port means connected to the piping to receive fuel from said supply, a pair of outlet port means connected by the piping to respective burners, and a pair of electrically operated valves disposed in operative normally closed relation to respective outlet port means, and means for supplying electrical potential to said valves simultaneously, the valve controlling flow of fuel to said second burner being operable at a predetermined time interval subsequent to the other.

11. A self-clean oven comprising an oven compartment to be heated, a first gas-fueled burner in the upper portion of the compartment, a second gas-fueled burner in the lower portion of the compartment, piping adapted to be connected at one end to a source of fuel and connected to said burners for supplying fuel thereto, ignition means adjacent each burner, and con-. trol means for delaying the supply of fuel to said second burner for a predetermined time interval subsequent supply of fuel to said first burner, said control means comprising valve means in said piping, said valve means having inlet port means connected to the piping to receive fuel from said supply, a pair of outlet port means connected by the piping to respective burners, and a pair of electrically operated valves each having a closure member disposed in operative normally closed relation to a respective outlet port means, a supporting member supporting said closure member and including a bimetallic element and means for heating the individual bimetallic elements to cause movement of said supporting members and consequent retraction of the closure members from the respective outlet port means, and means for supplying electrical potential to said heating means simultaneously, the valve controlling flow of fuel to said second burner being operable at a predetermined time interval subsequent to the other.

12. A self-clean oven as set forth in claim 11 wherein the closure member associated with the outlet port means which is connected to the second burner is retractable from the respective outlet port means at a predetermined time interval subsequent to retraction of the other closure member.

13. A self-clean oven as set forth in claim 12 wherein said pair of valves are located within a common housing.

14. A self-clean oven as set forth in claim 1 1 wherein the closure member associated with the outlet port means which is connected to the second burner engages its respective outlet port means witha pressure substantially in excess of the pressure with which the other closure member engages its respective outlet port means whereby the closure member applying greater pressure will require a longer period of time for movement away from its outlet port means.

15. A self-clean oven as set forth in claim 11 wherein said heating means comprises a pair of electrically en-' ergizable resistance heating elements located adjacent respective bimetallic elements.

16. A self-clean oven as set forth in claim 15 wherein the heating element associated with the valve which controls flow of fuel to the first burner is larger than the other heating element whereby it will function to heat its adjacent bimetallic element faster than the smaller heating element can heat its respective bimetallic element. 

1. A gas-fueled oven comprising a compartment to be heated, two spaced burners for heating said compartment, and means for supplying fuel to the burners at different time intervals, said means comprising valve means having inlet port means connected to a source of fuel, a pair of outlet port means, conduits connecting the outlet port means to respective burners, and a pair of electrically operated valves disposed in operative normally closed relation to respective outlet port means, and means for supplying electric potential to said valves simultaneously, one of said valves being operable at a predetermined time interval subsequent to the other.
 2. A gas-fueled oven comprising a compartment to be heated, two spaced burners for heating said compartment, and means for supplying fuel to the burners at different time intervals, said means comprising valve means having inlet port means connEcted to a source of fuel, a pair of outlet port means, conduits connecting the outlet port means to respective burners, a pair of electrically operated valves disposed in operative normally closed relation to respective outlet port means, said valves having different controlled operating characteristics whereby one thereof will open at a predetermined time interval subsequent to opening of the other, and means for supplying electrical potential to said valves simultaneously.
 3. A gas-fueled oven comprising a compartment to be heated, two spaced burners for heating said compartment, and means for supplying fuel to the burners at different time intervals, said means comprising valve means having inlet port means connected to a source of fuel, a pair of outlet port means, conduits connecting the outlet port means to respective burners, and a pair of valves each having a closure member disposed in operative normally closed relation to a respective outlet port means, a supporting member supporting said closure member and including a bimetallic element and means for heating the individual bimetallic elements to cause movement of said supporting members and consequent retraction of the closure members from the respective outlet port means.
 4. A gas-fueled oven as set forth in claim 3 wherein one of said supporting arms and closure members is retractable from the respective outlet port means at a predetermined time interval subsequent to retraction of the other arm.
 5. A gas-fueled oven as set forth in claim 4 wherein means is provided for supplying electrical potential to said heating means simultaneously.
 6. A gas-fueled oven as set forth in claim 3 wherein said pair of valves are located within a common housing.
 7. A gas-fueled oven as set forth in claim 3 wherein one of said closure members engages its respective outlet port means with a pressure substantially in excess of the pressure with which the other closure member engages its respective outlet port means whereby the closure member applying greater pressure will require a longer period of time for movement away from its outlet port means.
 8. A gas-fueled oven as set forth in claim 3 wherein said heating means comprises a pair of electrically energizable resistance heating elements located adjacent respective bimetallic elements.
 9. A gas-fueled oven as set forth in claim 8 wherein one of said heating elements is larger than the other whereby it will function to heat its adjacent bimetallic element faster than the smaller heating element can heat its respective bimetallic member.
 10. A self-clean oven comprising an oven compartment to be heated, a first gas-fueled burner in the upper portion of the compartment, a second gas-fueled burner in the lower portion of the compartment, piping adapted to be connected at one end to a source of fuel and connected to said burners for supplying fuel thereto, ignition means adjacent each burner, and control means for delaying the supply of fuel to said second burner for a predetermined time interval subsequent supply of fuel to said first burner, said control means comprising valve means in said piping, said valve means having inlet port means connected to the piping to receive fuel from said supply, a pair of outlet port means connected by the piping to respective burners, and a pair of electrically operated valves disposed in operative normally closed relation to respective outlet port means, and means for supplying electrical potential to said valves simultaneously, the valve controlling flow of fuel to said second burner being operable at a predetermined time interval subsequent to the other.
 11. A self-clean oven comprising an oven compartment to be heated, a first gas-fueled burner in the upper portion of the compartment, a second gas-fueled burner in the lower portion of the compartment, piping adapted to be connected at one end to a source of fuel and connected to said burners for supplying fuel thereto, ignition means adjacent each burner, and control means for delaying the supply of fuel to said second burner for a predetermined time interval subsequent supply of fuel to said first burner, said control means comprising valve means in said piping, said valve means having inlet port means connected to the piping to receive fuel from said supply, a pair of outlet port means connected by the piping to respective burners, and a pair of electrically operated valves each having a closure member disposed in operative normally closed relation to a respective outlet port means, a supporting member supporting said closure member and including a bimetallic element and means for heating the individual bimetallic elements to cause movement of said supporting members and consequent retraction of the closure members from the respective outlet port means, and means for supplying electrical potential to said heating means simultaneously, the valve controlling flow of fuel to said second burner being operable at a predetermined time interval subsequent to the other.
 12. A self-clean oven as set forth in claim 11 wherein the closure member associated with the outlet port means which is connected to the second burner is retractable from the respective outlet port means at a predetermined time interval subsequent to retraction of the other closure member.
 13. A self-clean oven as set forth in claim 12 wherein said pair of valves are located within a common housing.
 14. A self-clean oven as set forth in claim 11 wherein the closure member associated with the outlet port means which is connected to the second burner engages its respective outlet port means with a pressure substantially in excess of the pressure with which the other closure member engages its respective outlet port means whereby the closure member applying greater pressure will require a longer period of time for movement away from its outlet port means.
 15. A self-clean oven as set forth in claim 11 wherein said heating means comprises a pair of electrically energizable resistance heating elements located adjacent respective bimetallic elements.
 16. A self-clean oven as set forth in claim 15 wherein the heating element associated with the valve which controls flow of fuel to the first burner is larger than the other heating element whereby it will function to heat its adjacent bimetallic element faster than the smaller heating element can heat its respective bimetallic element. 